The design of earthing system for 230 kV substation is challenging task. A safety is one major concern in the operation and design of an electrical power system. This Paper is to provide information pertinent to safe earthing practice in substation design and to establish the safe limits of potential difference under normal and fault conditions. Substation earthing system design requires calculating of parameter such as touch and step voltage criteria for safety, grid resistance, maximum grid current, earth resistance, minimum conductor size and electrode size, maximum fault current level and soil resistivity. Soil resistivity is a major factor influencing substation grid design. In this paper, design of earthing grid for Square configuration to obtain the minimum cost and safety. Finally, simulation results were carried out using ETAP 12.6 software. This paper mentions the method proposed for substation earthing is in accordance with IEEE Std 80 2000. Khin Thuzar Soe | Thet Mon Aye | Aye Aye Mon "Design of Earthing System for 230 kV High Voltage Substation by ETAP 12.6 Software" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-5 , August 2019, URL: https://www.ijtsrd.com/papers/ijtsrd26747.pdf Paper URL: https://www.ijtsrd.com/engineering/electrical-engineering/26747/design-of-earthing-system-for-230-kv-high-voltage-substation-by-etap-126-software/khin-thuzar-soe
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III. DESIGN METHODOLOGY
The design procedure block diagram in Figure 1 is the sort
earthing studies of powernetworksandthealgorithmcanbe
expressed as follows:
Input data 𝜌,A
Compute the conductor size
Compute Touch and Step Voltage
Etouch,Estep
Compute first design of Grid D,n,L,h
Compute Grid Resistance Rg,Lc, Lr
Compute fault Current IG,If
Compute mesh and step voltage
Em,Es,Ki,Ks,Km,Kii,Kh
Detail design
Modify design D,n,LT
Em < Etouch
Es < Estep
ComputeIGRg<Etouch
Yes
No
Figure1. Block Diagram for Earthing Network Design
IV. STEPS OF DESIGN
Step 1: Start
Step 2: Substation Data
Data will be collected and important data from
substation.
Step 3: Calculation of conductor size
Cross section used for wireless networks based on land-
related equations, it is calculated and determined flow error
(3I0) the maximum amount must be injected into the
network during the probable future developments and
continuing up to times short circuit current (tf), which
includes the protection of backup is to be determined
equations 1 and 2.
)XXj(X)RR(R3R
V
3I
021021f
0
(1)
a0
m0
rrc
2mm
TK
TK
ln
ραt
4
10TCAP
I
A (2)
Step 4: Calculation of Tolerable step voltage and touch
voltage are based on (3 _ 6).
s
ssstep,50
t
0.116
)ρC6(1000E (3)
s
ssstep,70
t
0.157
)ρC6(1000E (4)
s
sstouch,50
t
0.116
)ρC1.5(1000E (5)
s
sstouch,70
t
0.157
)ρC5.1(1000E (6)
Step 5: Preliminary design parameters like distance
between equally spaced conductors, grid burial depth,
total length of horizontal conductors and number of
parallel conductors in one direction are determined.
Step 6: The grid resistance is determined by equation 7.
A
20h1
1
(1
20A
1
L
1
ρR
T
g (7)
Step 7: Calculation of grid current
The maximum grid current is determined by combining
decrement factor and symmetrical grid current is given by
equation 8 and 9.
f0g S3II (8)
)I(3SDI 0ffG (9)
Step 8: Calculation of the product of maximum grid
current and grid resistance
If it is less than the touch voltage,
touchgG ERI (10)
Step 9: The mesh voltage and step voltage are
determined by equation 11 and 12.
m
imG
m
L
KKIρ
E (11)
S
GiS
s
L
IKKρ
E (12)
Step 10: If the calculated mesh voltage is less than the
touch voltage then proceeds for step 9, otherwise
modify the design.
Step 11: If the calculated step voltage is less than the
step voltage then proceeds for detailed design,
otherwise modify the design.
Step 12: After calculating and determined all required
grid parameters detailed design is prepared.
V. SIMULATION AND TESTING RESULTS
The design of a substation groundingsystemis verycomplex
due to the number of involved phenomena. One of them
comes from the fact that lightning influences the local
resistivity of the soil given, whenlightningoccurs, non-linear
phenomena appear in the soil.
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@ IJTSRD | Unique Paper ID – IJTSRD26747 | Volume – 3 | Issue – 5 | July - August 2019 Page 1842
Figure2. Square Grounding Grid without Rods
Figure3. Touch and step Voltage Value in ETAP
Simulation
Nevertheless, this is not the only difference regarding the
low frequency case. Indeed, the high frequency response of
both grounding grids and human body are not the same for
fast transients and power frequency. In this section
simulations are carried out in order to verify the results
obtained through manual calculations. A software known as
ETAP PowerStation is used for the simulations. The
objectives of the program are:
To provide a low cost computer program running on a
personal computer.
To provide an easy to use, but technically acceptable
solution to the complex problem of grounding grid
design.
To design a safe, technically acceptable and
economically viable grounding grid.
Figure4. Square Grounding Grid with Rods
Figure5. Screenshot of ETAP Software
Figure6. Screenshot of ETAP Software
Figure7. Touch and Step Voltage Value in ETAP
Simulation
Table 1Design Parameters
Parameter
Without
Rods
With
Rods
Grid length
Lx 200ft 200ft
Ly 200ft 200ft
Number of
conductor
X-direction 11 11
Y-direction 11 11
Number of Rod - 44
Length of Rod - 30ft
Conductor depth 2ft 2ft
Step Voltage 551.6 461.6
Touch Voltage 923.9 360.2
GPR 5365.5 4592.8
Ground Resistance Rg 0.634 0.543
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@ IJTSRD | Unique Paper ID – IJTSRD26747 | Volume – 3 | Issue – 5 | July - August 2019 Page 1843
VI. CONCLUSIONS
In this grounding system for high voltage substation has
been designed and the results are obtained by ETAP
software. Construction of earthing grid is expressed in here.
The step and touch voltages are dangerous for human body.
Human body may get electric shocks from step and touch
voltages. The final design shows that the resultanttouch and
steps voltages are within tolerable regions and no more
enhancements are necessary.Otherdesignmodifications are
useful in obtaining specific results. Rods are only effective in
two layer soils. Reducing the mesh sizeis anadmirabletouch
voltage reduction factor and when accompanied by a
reduction in the overall ground resistant assist in reducing
the step voltage.
ACKNOWLEDGEMENT
The author is grateful to her Rector, Dr. Kyi Soe, Rector of
West Yangon Technological University. And also special
thanks to Dr. Min Thu San, Head of Electrical Power
Engineering Department, Dr. Thet Mon Aye, Lecturer, West
Yangon Technological University, Daw Aye Aye Mon,
Assistant Lecturer, West Yangon Technological University.
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